A sheet heater includes a first fiber layer, a second fiber layer distanced from the first fiber layer, a third fiber layer disposed between the first and second fiber layers, and a controller operable to control heat generation. The first fiber layer is constituted of first conductive portions and first non-conductive portions. The second fiber layer is constituted of second conductive portions and second non-conductive portions. The third fiber layer includes functional layers each constituted of connecting yarns and non-functional layers arranged to insulate each of the functional layers from others of the functional layers. The controller applies voltage between the first and second conductive portions to heat the connecting yarns. According to the heater, a desired temperature distribution can be created on the heater by applying the voltage selectively to one target segment composed of the first conductive portion, the functional layer and the second conductive portion.